1. Field of the Invention
The present invention relates to an Fe based soft magnetic alloy. Further, the present invention relates to magnetic materials containing such a soft magnetic alloy, for example, ribbons, compressed powders and the like as well as to a process and apparatus for producing such magnetic materials. Also, the present invention relates to magnetic transducers such as a magnetic head, a transformer and a choke coil. However, the present invention is also useful in other applications.
2. Description of Related Arts
Soft magnetic alloys used in magnetic heads, transformers. choke coils and the like must generally have the following characteristics:
(1) They have a high saturated magnetic flux density. PA1 (2) They have a high permeability. PA1 (3) They have a low coercive force. PA1 (4) They can be shaped into a thin material. PA1 (5) They have a high hardness. PA1 0.ltoreq.a.ltoreq.0.05 atomic %, PA1 0&lt;b.ltoreq.93 atomic %, PA1 0.5.ltoreq.x.ltoreq.16 atomic %, PA1 4.ltoreq.y.ltoreq.10 atomic %, PA1 0.ltoreq.z.ltoreq.4.5 atomic % PA1 heating an Fe-based soft magnetic alloy having a high saturated magnetic flux density and having a composition represented by formula (I) as defined above at a temperature no lower than a crystallization temperature, and PA1 cooling the alloy at a cooling rate of no lower than 100.degree. C./minute. PA1 heating an Fe-based soft magnetic alloy having a high saturated magnetic flux density and having a composition represented by formula (I) as defined above at a temperature no lower than a crystallization temperature to render it brittle, and PA1 pulverizing the alloy. PA1 providing a molten metal of an Fe-based soft magnetic alloy having a composition represented by formula (I) as defined above, PA1 providing an evacuatable chamber, PA1 housing a nozzle for ejecting the molten metal and a cooling roll in the evacuatable chamber, PA1 establishing vacuum in the evacuatable chamber, PA1 ejecting the alloy through the nozzle onto a surface of the cooling roll while the roll is being rotated in a predetermined direction, the nozzle being associated with the cooling roll with a tip of the nozzle being arranged in the vicinity of the surface of the cooling roll at a predetermined distance therefrom, to form a ribbon of the alloy, and PA1 withdrawing the ribbon in the same direction as that in which the cooling roll is rotated.
On the other hand, magnetic heads must have the following characteristics in addition to (1) to (4) above from a point of view of abrasion resistance:
Accordingly, when producing soft magnetic alloys or magnetic heads, extensive investigations on the physical properties of various alloy compositions have been made taking into consideration the above-described points.
Heretofore, for the aforementioned purposes, there have been used crystalline alloys such as Sendust, Permalloy (50% Ni--Fe Permalloy, 80% Ni--Fe Permalloy, etc.), and silicon steel (see for example, Japanese Patent Publication Nos. 37688/1987 and 45285/1987). Recently, Fe-based or Co-based amorphous alloys have also been used.
In the case of magnetic heads, however, their has been a growing demand for magnetic materials suitable for high performance magnetic heads in order to cope with a recent trend toward magnetic recording media having a higher coercive force thereby keeping pace with a recent shift toward higher density recording. As for transformers and choke coils, high performance magnetic materials are desired because further miniaturization thereof is required to meet with miniaturization of various electronic devices.
However, the aforementioned Sendust has a defect in that its saturated magnetic flux density is as low as about 11 kG while it has an excellent soft magnetic characteristics. Similarly, Permalloy has a defect in that it has a low saturated magnetic flux density as low as about 8 kG when it has an alloy composition which exhibits excellent soft magnetic characteristics. More particularly, when it is applied to magnetic cores, core loss at high frequencies is large and the temperature of the core increases drastically at a frequency of no less than several tens kHz, resulting in that it is difficult to use as a material for magnetic cores. Silicon steel has a high saturated magnetic flux density but it has a poor soft magnetic characteristics. Also it is disadvantageous in that its iron loss is not low enough and thus it is unsatisfactory from a point of view of energy saving and has a problem with heat generation when used in transformers.
On the other hand, as for the amorphous alloy, Co-based amorphous magnetic cores have been increasingly used as cores for controlling switching power source, making the most of their features of having a low core loss at high frequencies and having a high squareness.
However, the Co-based amorphous alloys have problems in that not only they are costly because their constituent raw materials are expensive but also they have a low saturated magnetic flux density at a frequencies in zone of several tens kHz to 100 kHz and therefore they suffer from limited working magnetic flux density, thus making it difficult to sufficiently miniaturize magnetic cores.
Fe-Based alloys generally have a high saturated magnetic flux density and those having a saturated magnetic flux density of 15 kG or higher can be obtained but they have insufficient soft magnetic characteristics. It is known that Fe-based amorphous alloys give rise to magnetic cores having a high squareness ratio of a direct current B-H curve and a high maximum permeability can be obtained as described in Japanese Patent Publication No. 1183/1983.
However, magnetic cores made of the above-described Fe-based amorphous alloys have a large iron loss and efforts have been made to improve the iron loss by adjusting additive elements. However, in spite of these efforts, Fe-based amorphous alloys still have a large iron loss as compared with Co-based amorphous alloys. In addition, Fe-based amorphous alloys have an extremely large magnetic strain and are sensitive to stress. Therefore, they have a problem that their magnetic characteristics tend to deteriorate due to deformations as a result of mechanical vibration or by the weight of the alloys themselves.
Turning to an apparatus for producing magnetic materials, FIG. 1 shows a conventional apparatus for continuously producing a ribbon made of an amorphous alloy according to a so-called single roll method. The apparatus has a cooling roll 1 made of Cu which is rotated at a high speed and a nozzle 2 arranged in the vicinity of a top portion of the roll 1 which sprays a molten metal 3 onto the roll 1 thereby quickly cooling the molten metal 3 on the surface of the cooling roll 1 and solidifying it so that a ribbon can be formed, ribbon is drawn in a direction in which the cooling roll 1 rotates.
In the apparatus shown in FIG. 1, the surface of the cooling roll 1 is mirror surface-finished, the nozzle 2 is provided substantially vertically at a top portion of the cooling roll 1, with the distance between the tip of the nozzle and the surface of the cooling roll 1 being set to about 1 mm or less. The molten metal 3 discharged from the nozzle 2 forms a puddle 4 which is substantially stationary between the tip of the nozzle 2 and the surface of the cooling roll 1. As the cooling roll 1 rotates, the molten metal 3 is drawn out from the puddle 4 and cooled on the surface of the cooling roll 1 to be solidified in the form of a belt or ribbon, thus continuously forming a ribbon 5.
In this case, soft magnetic alloys generally used as a material for making magnetic heads are required to have a sufficiently smooth surface, that is, their surface roughness must be sufficiently small. However, ribbons produced by the conventional apparatus fail to always have a surface roughness small enough to be useful for acoustic magnetic heads and accordingly it has been strenuously demanded to develop an apparatus for producing an alloy ribbon which can give rise to smooth surfaces.
A further problem of the conventional apparatus is that ribbons produced thereby have a surface roughnesses which fluctuates between both surfaces. More specifically, in comparison with the roll contacting surface, which is formed while the molten metal is being solidified in contact with the cooling roll, the free solidification surface, which is formed by solidification of the molten metal without contact with the roll, has a relatively large surface roughness. Because of this defect, it is difficult to use the ribbons as a material for making magnetic heads.
Furthermore, in the case where ribbons are produced from a soft magnetic alloy mainly composed of Fe, there is a fear that the ribbons tend to be oxidized after quenching. Accordingly, there has also been a demand to produce Fe-based soft magnetic alloy ribbons without being oxidized.